1. Field of the Invention
The present invention relates to a method and apparatus for embedding and presenting tissue samples for histological examination and, more particularly, a method for preparing a tissue sample for microscopic examination.
2. Prior Art
A procedure for preparing tissue samples for microscopic examination by embedding the tissue in paraffin and slicing the paraffin-embedded tissue into thin layers with a microtome for mounting on a slide is well known in the art. Preparatory to embedding, the tissue is pretreated in various solutions selected in accordance with the particular examination being conducted. Typically, prior to paraffin embedding, the tissue sample is fixed, dehydrated, cleared, infiltrated with molten paraffin and, depending on the test, stained.
In order to impregnate the tissue sample, the sample is dehydrated, most commonly with isopropyl alcohol, and then immersed in liquid paraffin. The step of paraffin impregnation normally takes place at ambient pressure and at a temperature slightly higher than the melting point of the embedding material. In the event that the embedding material is paraffins, the melting point lies approximately between 50 degrees C. and 58 degrees C. The replacement of the isopropyl alcohol contained in the tissue of the tissue samples with paraffin is effected by dissolving the isopropyl alcohol in paraffin such that the concentration of the paraffin increases in the tissue sample. When the paraffin solidifies, thin sections can be sliced from the tissue samples embedded in paraffin block, mounted on a slide and examined under a microscope.
Berger, in U.S. Pat. No. 5,089,288, discloses a method of impregnating a tissue sample with paraffin in which a tissue sample, which has been fixed with isopropyl alcohol, is maintained under vacuum in a treatment vessel and the molten paraffin and tissue sample are simultaneously subjected to ultrasonic vibration effective to remove the isopropyl alcohol from the tissue sample and to impregnate the tissue sample with the paraffin.
McCormick, in U.S. Pat. No. 5,665,398, discloses a system for providing an embedded tissue specimen subsequent to fluid treatment of the specimen and preparatory to histological examination. The system includes the combination of a cassette for use in the preparation of tissue specimens for histological examination and an embedding mold having a first cavity for receiving the treated specimen and a second cavity for receiving the cassette. The system includes means for dispensing a predetermined amount of molten wax into the embedding mold.
U.S. Pat. No. 5,080,869 to McCormick describes a cassette for efficiently processing tissue samples. The cassette is stackable and can be used for preparing a plurality of specimens. The cassette generally includes a plurality of apertures disposed in the walls of the cassette for passage of processing fluids in a direction both orthogonal and parallel to the plane of the bottom wall of the cassette. The cassette also includes a sloping extension of the front wall of the cassette for ease in placing indicia on the cassette for identification of the sample. Further examples of systems and methods useful for preparing paraffin-impregnated tissue samples for histological examination are disclosed in U.S. Pat. Nos. 5,843,700 to Kerrod, et al., and 4,569,647 to McCormick.
A problem with the prior art methods of embedding and sectioning tissue is the clumping of cells such that cells of interest may not be present in a particular field of view. It is, therefore, desirable to have a method for preparing tissue for sectioning such that cells comprising the tissue are more or less evenly distributed on the section mounted on a slide thereby improving the probability of a particular cell type of interest being present in a particular section and field of view.
It is a first object of the invention to provide a method for processing a tissue sample for mounting on a slide.
It is a further object of the invention to provide a method for preparing a tissue for sectioning wherein the cells comprising the tissue are substantially evenly distributed throughout the tissue preparation and a tissue section derived therefrom.
It is yet a further object of the invention to provide an apparatus and method for using the apparatus operable for preparing and presenting a tissue for sectioning.
It is an overall object of the invention to provide a method and apparatus for preparing a tissue sample for examination wherein the probability of a cell of interest being disposed within a field of view of the examiner is enhanced when compared with prior art methods of tissue sample preparation.
The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: